(1) Field of the Invention
The present invention relates to an LCD panel and the fabricating method thereof, and more specifically to a method for fabricating an LCD panel by means of PSA (polymer stabilized alignment) technology.
(2) Description of the Prior Art
Due to rapid development in the display technology, an LCD (liquid crystal display) device is generally preferred when compared to the conventional CRT-type display device due to its compact size and quick response time in addition to its lower power consumption and low radiation. Therefore, the LCD device is in great demand in the market and is widely used in many electronic devices, such as calculators, PDAs, notebook computers, digital cameras and mobile phones.
The LCD device manufacturers have devoted a tremendous effort in the research to improve the ability of the LCD device and lower the cost simultaneously. Therefore, the demand for the LCD device is increasing. Presently, the research is emphasized in the field how to widen the viewing angle of the LCD panel and shorten the response time for displaying the image.
In order to achieve the aforesaid objects, the LCD manufacturers have introduced a method for fabricating the LCD device utilizing the PSA (polymer stabilized alignment) technology.
The method is to form polymers within the liquid crystal layer for influencing the liquid crystal molecules in the liquid crystal layer to extend in a pretilt angle. Thus, when the voltage is applied onto the pixel electrode, an electric field is generated that forces the liquid crystal molecules in the liquid crystal layer to change their orientation from the pretilt angle to an appropriate angle, thereby shortening the response time. For better understanding of the method, a basic structure of an LCD panel is introduced below.
The LCD device generally includes a liquid crystal layer sandwiched between an upper substrate and a lower substrate. A common electrode is sandwiched between the liquid crystal layer and the upper substrate.
FIG. 1 shows a pixel structure of a conventional PSA LCD panel formed on a lower substrate, and includes a plurality of pixel units 10. Each pixel unit 10 includes a scan line 101, a data line 102, a thin film transistor 103, a storage capacitor Cst, and a pixel electrode 105. During the working operation, the scan line 101 is capable of scanning a scan signal through the transistor 103 so as to permit transmission of the voltage signal from the data line 102 to the pixel electrode 105. At the same time, since the voltage level fed through the data line 102 is still retained within the storage capacitor Cst, the pixel unit 10 can be kept under a preset gray value during the break of the data transmission.
As illustrated, the pixel electrode 105 includes a pattern having a plurality of parallel ribs extending from a center to four corners thereof (the pattern has a fish-bone configuration). Under the operation, an electric field is resulted between the pixel electrode 105 and the common electrode so as to force the liquid crystal molecules to change their orientation. The liquid crystal molecules change their orientation towards the four corners due to the configuration of the pixel electrode 105 so as to form four domains with respect to the center thereof.
In order to shorten the response time for displaying the image, after forming of the aforementioned the pixel electrode 105 in the aforesaid manner, a curing process is conducted utilizing the PSA (polymer stabilized alignment) technology so as to direct the liquid crystal molecules within the liquid crystal layer in a pretilt angle. FIG. 2 illustrates a circuit diagram of a prior art pixel unit 10 during the curing process. The circuit diagram includes the aforementioned storage capacitor Cst, and a liquid crystal capacitor Clc, wherein the liquid crystal capacitor Clc is formed by the pixel electrode 105 and a common electrode. The common electrode is kept at a predetermined voltage level during the curing process. Preferably, the common electrode is grounded (kept at the ground voltage level Vground).
In the fabricating process of the LCD device, after adding monomers for polymer orientation into the liquid crystal layer, the curing process is performed to apply a curing voltage Vcuring onto the storage capacitor Cst such that the pixel electrode 105 may have a coupling voltage Vcouple due to the capacitor coupling, thereby turning the liquid crystal molecules to tend in a pretilt angle with the monomers tending the same direction. An ultra violet light is then applied so as to enable the monomers to combine together to form the polymers tending in the predetermined inclined angle.
When no voltage is applied onto the liquid crystal layer, the liquid crystal molecules tend in the pretilt angle under the influence of the polymers. When driven by an electric field, the liquid crystal molecules can turn swiftly from the pretilt angle into the appropriate position, thereby shortening the response time for displaying the image.
Presently, the pixel electrode 105 in the PSA LCD panel is made from ITO (indium tin oxide). Lithographic and etching processes are conducted to form the pattern with the fish-bone configuration having a plurality of parallel ribs divided in four domains, which, in turn, provides a higher contrast, a higher brightness and a shorter response time. However, it is in the trend to produce the LCD panel in a larger dimension, the aforesaid design is unable to solve the color-shift problem in changing view and to reduce the color washout phenomenon.